The ejection distribution of solvated electrons generated by the one-photon photodetachment of aqueous I- and two-photon ionization of the solvent
The ejection distribution of solvated electrons generated by the one-photon photodetachment of aqueous I- and two-photon ionization of the solvent
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DOI：
10.1063/1.1309011
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发表时间：
2000-10-15
影响因子：
4.4
通讯作者：
Bradforth, SE
中科院分区：
文献类型：
--
作者：
Kloepfer, JA;Vilchiz, VH;Bradforth, SE
比较了水溶液中I-离子单光子电离后的超快动力学和溶剂双光子电离后的超快动力学。使用50秒紫外脉冲的超快泵浦-探针实验揭示了电子喷射的相似且非常快速的时间尺度。然而，从泵入导带的水和从阈值分离的碘离子的电子喷射过程是容易区分的。利用两种不同的模型重建了观察到的皮秒时间尺度的双生子复合和电子逃逸动力学，一种是扩散限制的电子从类似于15埃的地方返回到它的母体，另一种是由反向电子转移速率控制的竞争动力学模型。我们得出结论，在卤化物分离中“弹出”的电子仅仅是从同一溶剂壳层中的卤素原子中分离出来的。分离到接触对的分配是基于复合轮廓，而不是基于接触对中电子的任何新光谱吸收的假设。接触对的寿命惊人地长，而考虑到偶的邻近性，非绝热复合相当缓慢。在混合溶剂中的实验证实了我们对两种不同的喷射机制的指派。因此，共振（单光子）电荷转移到溶剂（CTTS）过程中的分离机制与水碘离子的多光子分离有根本区别，后者更类似于直接溶剂电离。(C) 2000年美国物理研究所。[S0021 - 9606(00) 51239 - 2]。
The ultrafast dynamics following one-photon UV photodetachment of I- ions in aqueous solution are compared with those following two-photon ionization of the solvent. Ultrafast pump-probe experiments employing 50 fs ultraviolet pulses reveal similar and very rapid time scales for electron ejection. However, the electron ejection process from water pumped into the conduction band and from iodide ions detached at threshold are readily distinguishable. The observed picosecond timescale geminate recombination and electron escape dynamics are reconstructed using two different models, a diffusion-limited return of the electron from similar to 15 Angstrom to its parent and a competing kinetics model governed by the reverse electron transfer rate. We conclude that the "ejected" electron in the halide detachment is merely separated from the halogen atom within the same solvent shell. The assignment of detachment into a contact pair is based on the recombination profile rather than by the postulate of any new spectral absorption due to an electron in a contact pair. The contact pair is surprisingly long-lived and the nonadiabatic recombination is rather slow considering the proximity of the partners. Experiments in mixed solvents confirm our assignment of the two distinct ejection mechanisms. The detachment mechanism is therefore fundamentally different in the resonant (one photon) charge-transfer-to-solvent (CTTS) process from the multiphoton detachment of aqueous iodide ions, which bears more similarity to the direct solvent ionization. (C) 2000 American Institute of Physics. [S0021- 9606(00)51239-2].